The driver of a charter bus that overturned in San Marcos early Friday fell asleep behind the wheel and then tried to overcorrect, according to an accident report released by the San Marcos Police Department today.

An investigation is ongoing, police say, but an initial investigation by Officer Andrew Sparenberg determined that Jesus Basio-Ramirez of Dallas nodded of behind the wheel, precipitating the early morning crash.

At 4:15 a.m., the bus was traveling northbound on Interstate 35 when it lost control and tipped over near mile marker 199 at Posey Road in south San Marcos, blocking all three lanes of traffic.

“The bus ran off the road to the right, overcorrected and rolled over onto its side,” San Marcos Police Chief Howard Williams said. “It was literally stretched out across the expressway.”

The bus, owned by Dallas-based Mares Bus Lines Inc., had 21 passengers and was traveling from Laredo to Dallas. The bus had just made a stop in New Braunfels before the crash, police say.

Injured passengers were transported with non-life threatening injuries to hospitals in Austin, San Marcos and San Antonio. Three of the injured had to be airlifted, Williams said.

The worst injury sustained was by a four-year-old girl who suffered a severe broken leg. A hospital official later confirmed that the girl’s leg had to be amputated at Dell Children’s Hospital in Austin.

“It was obviously a nasty injury for her,” Williams said.

Williams added that three passengers were able to walk away uninjured from the crash site. Around 9 a.m., the northbound part of the interstate reopened. The exact cause of the crash is still under investigation. Mares Bus Lines could not be reached for comment.

According to the Federal Motor Carrier Safety Administration, the bus company had a slew of violations to its fleet of nine vehicles and 13 drivers during a two-year safety record ending on May 20.

Violations include:

81 maintenance violations. The seven most serious violations that put vehicles out of service involved tires, brake hosing, defective lamps and improper wiring protection. The company recently scored a 55.7 percent in road performance, which is below the threshold of 65 percent.

Five violations for unsafe driving that involved improper lane change and speeding

12 violations for fatigued driving

one crash with three injuries on Jan. 11

two drivers without a commercial driver’s license

San Marcos police are the lead investigators in Friday’s crash. A number of other emergency agencies also responded to the scene, located close to the Hays-Comal county line, including the San Marcos and New Braunfels fire departments, San Marcos/Hays County Emergency Medical Service, Department of Public Safety, and the Hays and Comal county sheriff’s offices.